The Lotus angustissumus Group (Fabaceae): Can Phylogenetic Patterns Be Accommodated by a Taxonomic Concept?

The Lotus angustissimus group represents an example of obvious contradictions between the molecular and morphological data. This group includes from six to eight mostly annual species of Lotus section Lotus, with the center of species diversity in the Mediterranean. We performed a phylogenetic analysis of the genus Lotus with an expanded representation of all known species of the L. angustissimus group using both nuclear (nrITS) and a set of plastid DNA markers and compared the results with traditional taxonomy of this group. Our results demonstrated a non-monophyletic nature of the study group. In addition, the nrITS and plastid dataset tree topologies were incongruent with each other in both Bayesian and ML analyses. We revealed very complex phylogenetic relationships among the species of the group. Important results obtained in this study are: (1) genetic and geographical differentiation in the latitudinal direction (between L. angustissimus and L. praetermissus) and in the longitudinal direction among closely related accessions identified as L. castellanus, L. lourdes-santiagoi and L. palustris; (2) close genetic links between the Anatolian endemic L. macrotrichus and L. praetermissus from Eastern Europe and Central Asia; and (3) the hybrid nature of L. subbiflorus with L. parviflorus as its presumed male parent species. These results are discussed in the context of morphology, biogeography and taxonomy.